A one time optical information-recording medium (optical disc) capable of recording information by laser beams have been conventionally known. This optical disc is also called a direct read after write CD (so-called CD-R), and the typical structure of CD-R comprises a transparent disc-like support having provided thereon a recording layer containing an organic dye, a light-reflecting layer comprising metal, e.g., gold, and a protective layer of resin in this order from the support in lamination. Recording of information on CD-R is performed by irradiating CD-R with near infrared laser beams (laser beams of wavelength of near 780 nm, in general), the temperature of the irradiated part of the recording layer locally increases by absorbing the laser beams, and physical or chemical changes are caused (e.g., formation of pits) to alter the optical characteristics of the recording layer, thereby information is recorded. On the other hand, readout (reproduction) of information is also performed by the irradiation of laser beams of the same wavelength as used for recording. Information is reproduced by the detection of the difference in the reflectance between the part where the optical characteristics of the recording layer altered (recorded part) and the part where the optical characteristics did not alter (non-recorded part).
Optical recording media having higher recording density are demanded in recent years. To meet such a demand, optical discs referred to as direct read after write digital versatile discs (so-called DVD-R) are on the market. The DVD-R has the structure comprising a transparent disc-like support having pre-groove for tracking irradiation laser beams formed as narrow as half or less (from 0.74 to 0.8 μm) of that of CD-R, having provided thereon a recording layer comprising a dye, generally a light-reflecting layer on the recording layer, and if necessary a protective layer, and two sheets of this disc are adhered, or this disc and a protective support of the same form with the disc are adhered with an adhesive with the recording layer inside. The recording and reproduction on DVD-R are performed by irradiation with visible laser beams (generally laser beams of the wavelength of from 630 to 680 nm), and it is said that recording of higher density than with CD-R is possible. As the dyes used in the materials of optical recording discs, metal azo chelate dyes formed from an azo dye and a metal are disclosed. Representative examples of the metal azo chelate dyes are disclosed in the patent literatures, such as JP-A-63-9577, JP-A-63-9578, JP-A-63-9579, JP-A-3-268994, JP-A-8-156408 and JP-A-9-277703. (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.)
In recent years, networks such as Internet and high vision TV have spread rapidly. Further, broadcasting of HDTV (High Definition Television) is near at hand, so that the demands for recording media of high capacity for recording image information inexpensively and simply are increasing. Although DVD-R has secured the position as high capacity recording medium to some degree, it cannot be said that DVD-R has sufficiently great recording capacity capable of coping with the demands in the future. Accordingly, the development of optical discs having higher recording capacity has been advanced by the improvement of recording density with laser beams of shorter wavelength than DVD-R.
In an optical information-recording medium having a recording layer containing an organic dye, a recording and reproducing method of performing recording and reproducing of information by irradiating laser beams of the wavelength of 530 nm or less from a recording layer side toward a light reflecting layer side is disclosed. Specifically, a recording and reproducing method is proposed, which performs recording and reproducing of information by irradiating an optical disc containing, as the dyes of the recording layer, a porphyrin compound, an azo dye, a metal azo dye, a quinophthalone dye, a trimethine cyanine dye, a dicyanovinylphenyl skeleton dye, a coumarin compound, and a naphthalocyanine dye with blue (wavelength 430 nm, 488 nm) or blue-green (wavelength 515 nm) laser beams.